Cement-mortar lined carbon steel pipe and tubular goods are widely used in utility plants, residential and industrial water gathering and supply piping systems where corrosion is a concern. Pipes of 24" (610 mm) diameter or smaller are commonly joined by either partial penetration butt welding where asbestos gaskets are used to fill the space or gap between the cement-mortar lining of the mating pipe ends, or by use of weldable, threaded, plastic or other specialty couplings, including flanges. While these methods are acceptable for low pressure service (150 psig maximum), they are not acceptable for high pressure water injection service where operating pressures can be on the order of several thousand psig.
Successful and economical in-situ lining of long sections of existing and newly constructed pipelines for high pressure water injection service in the oil and gas industries has mandated the development of a reliable joining method that results in full penetration, good quality (code acceptable) welds and effective joint seals for the concrete lining.
One object of this invention is to provide an improved method for the reproducible fabrication of a high quality field weld and effective seal of tie-in joints for in-situ cement-mortar lined pipelines in high pressure water injection service. Another object of the invention is to achieve such welds economically in terms of both time and materials.
These objectives are achieved by the use of an inexpensive cylindrical carbon steel beveled backing ring of special design to enable full penetration butt welds to be obtained by a pipeline welder of average experience. In addition, the beveled ends of the backing ring function to:
(a) facilitate alignment and fit-up of the mating male and female ends of the cemented pipeline sections;
(b) prevent formation of a stress riser between the end of the backing ring and the adjacent cement-mortar lining; and
(c) provide an effective anchor for, and increase the contact surface area of, the grout joint seal.
The adjacent ends of the cement lining are also externally beveled to facilitate an improved sealing of the joint through the use of a heat expanding grout.